Numerous devices are available as object position detectors for use in computer systems and other applications. The most familiar of such devices is the computer mouse. While extremely popular as a position indicating device, a mouse has mechanical pans and requires a surface upon which to roll its position ball. The mouse translates movement of the position ball across the rolling surface as input to a computer. The growing popularity of laptop or notebook computers has created a significant problem for mouse type technologies which require a rolling surface. Laptop computers are inherently portable and designed for use in small confined areas such as, for example, airplanes, where there is insufficient room for a rolling surface. Adding to the problem is that a mouse usually needs to be moved over long distances for reasonable resolution. Finally, a mouse requires the user to lift a hand from the keyboard to make the cursor movement, thereby upsetting the prime purpose, which is usually typing on the computer.
As a result of the proliferation of laptop computers and the standardization of the Windows operating environment, a need for a reliable, portable, and integrated form of mouse control has arisen. To satisfy this need, mechanical ball or shaft rolling technologies, such as, for example, track balls have been designed for use with laptop computers. A track ball is similar to a mouse. A major difference, however is that, unlike a mouse, a track ball does not require a rolling surface. Track balls first appeared as clip-on attachments for laptop computers and then later were integrated within laptop computers.
A track ball is large in size and does not fit well in a volume-sensitive application such as a laptop computer. Furthermore, a track ball is quite cumbersome because it requires practiced dexterity by the user as he or she interacts with the device. Finally, a track ball is not durable and is easily subjected to contamination from environmental factors such as dirt, grease, and the like.
A. Cursor Control with Touchpads
Touchpads are pointing devices used for inputting coordinate data to computers and computer-controlled devices. A touchpad is typically a bounded plane capable of detecting localized pressure on its surface. A touchpad may be integrated within a computer or be a separate portable unit connected to a computer like a mouse. When a user touches the touchpad with a finger, stylus, or the like, the circuitry associated with the touchpad determines and reports to the attached computer the coordinates or the position of the location touched. Thus, touchpads may be used like a mouse as a position indicator for computer cursor control. Several types of touchpads are known in the art such as capacitive and resistive touchpads.
1. Capacitive Touchpads
Capacitive touchpads react to a capacitive coupling between an object placed near or on the surface of the touchpad and capacitors formed within the touchpad. For instance, U.S. Pat. No. 5,374,787 issued to Miller et al. and assigned to Synaptics, Inc., discloses a capacitive touchpad having two thin layers of electrically conductive lines or traces. A first set of traces runs in a first direction and is insulated by a dielectric insulator from a second set of traces running in a second direction generally perpendicular to the first direction. The two sets of traces are arranged in a crosswise grid pattern. The grid formed by the traces creates an array of capacitors that can store an electrical charge.
When a conductive object such as a finger or a metal stylus approaches or touches the touchpad, the capacitance of the capacitors are altered due to capacitive coupling between the object and the capacitors. The degree of alteration depends on the position of the object with respect to the traces. As a result, the location of the object in relation to the touchpad can be determined and monitored as the object moves across the touchpad.
Similarly, U.S. Pat. No. 3,921,166 issued to Volpe discloses a capartive matrix or grid in which an object such as a finger changes the transcapacitance between row and column electrodes.
Another variation of the capacitive touchpad is shown in U.S. Pat. No. 4,550,221 issued to Mabusth. The Mabusth patent discloses a capacitive touchpad having a substrate that supports first and second interleaved, closely spaced, non-overlapping conducting plates. The plates are aligned in rows and columns so that edges of each plate of an array are proximate to, but spaced apart from, the edges of plates of the other array. The first and second arrays are periodically connected in a multiplexed fashion to a capacitance measuring circuit which measures the change in capacitance in the arrays. In effect, the Mabusth patent discloses a grid of pixels which are capacitively coupled.
Capacitive touchpads suffer from many disadvantages. First, they are extremely sensitive to moisture contamination. As an object such as a finger moves over the touchpad, the moisture present in the skin disturbs the capacitor grid and measurements made from the disturbance determines the position of the finger. The operation of capacitive touchpads is, therefore, easily compromised in moist or damp environments or by perspiration of the user. In short, with moisture, capacitive touchpads become confused and lose their sensitivity.
Second, capacitive touchpads demand a constant power supply, offering no sleep mode option. Most capacitive touchpads draw a constant electrical current of 2.5 to 10 milliamps whether or not they are in use. With laptops, cordless keyboards, and even hand-held remote controls, battery life is a major concern. A touchpad that demands constant power is a major liability.
Third, capacitive touchpads are prone to inadvertent cursor positioning because they sense an object as it gets near their surface. This is problematic for the user because if the touchpad is installed near where the thumbs of the user naturally rest while typing, an inadvertent thumb simply moving over and above the touchpad can cause a false click and an unintended change in the cursor position. This can result in repeated, accidental repositioning of the cursor and high levels of user frustration. The user may also experience fatigue and extreme discomfort from intentionally holding his thumbs or fingers away from the touchpad to avoid false clicks.
Fourth, the electronic circuitry of capacitive touchpads is complex and expensive. Capacitive touchpads use a microprocessor for communicating with a computer. Between the touchpad and the microprocessor, electronic circuitry such as a semi-custom or fully-custom mixed signal gate array incorporating both analog and digital sections is provided. The cost of this circuitry is significant and, in most cases, higher than the cost of the microprocessor.
Fifth, capacitive touchpads indirectly measure the amount of applied pressure by measuring the surface area of the object applying the pressure. For instance, a capacitive touchpad measures the area of contact between a finger and the touchpad. Once that area is measured, relative pressure is determined by the change in the area over time. Illustratively, as a user pushes harder with his finger, more area is in contact and the touchpad estimates a greater pressure. Obviously, for applications such as signature capture, pressure-controlled scrolling and acceleration, 3D control, and the like, measuring the contact area to estimate the pressure is greatly inferior to measuring the actual pressure directly.
2. Resistive Touchpads
U.S. Pat. No. 5,521,336 issued to Buchanan et al. discloses a typical resistive touchpad. The disclosed resistive touchpad is a shunt mode device where electrons flow between interdigitating conductive traces when the traces are pressed together. A voltage potential between the interdigitating traces causes electrical current to flow through the traces at the point where the traces are in electrical contact. The location of the contact is determined using banks of drivers and receivers which scan the resistive touchpad.
Resistive touchpads may include a resistive layer separating the interdigitating traces at the point of contact. Thus, when a pair of traces are pressed together against the resistive layer at a location, electrical current flows from one trace through the resistive layer to the other trace at that location.
Resistive touchpads such as that disclosed by Buchanan et al. suffer from many disadvantages. First, resistive touchpads can only measure ON/OFF resistance. Thus, they cannot measure gradation in pressure and cannot be used for such applications as signature capture, pressure-controlled scrolling and acceleration, 3D control, and the like.
Second, the electronic circuitry of resistive touchpads is complex and expensive. Like capacitive touchpads, resistive touchpads have a microprocessor for communicating with a computer. Between the touchpad and the microprocessor, complex circuitry such as the banks of drivers and receivers shown in Buchanan et al. are provided. The cost of this circuitry is significant and, in most cases, higher than the cost of the microprocessor.
Third, resistive touchpads require a relatively significant force to activate, roughly about twenty grams of force. Unfortunately for the user, pushing his or her finger or a stylus against a touchpad at twenty grams of force is fatiguing.
B. Touchpads as Input Devices
In addition to cursor control, touchpads are also employed for providing control signals to a computer to perform functions associated with the location pressed on the touchpad. Typically, one or more regions of a touchpad are assigned to certain functions. The user is made aware of the function associated with each region by a template. A template is a sheet with a graphic design and is placed over and in contact with the touchpad surface. The graphic design maps out regions of the touchpad surface which are labelled to provide a reminder to the user as to the functions associated with the regions.
As an input device, a touchpad functions similarly to a mouse. For instance, a mouse generally has at least one mouse button for accomplishing mouse controlled functions such as menu pull down and selection, icon selection and use, and the like. Sometimes more buttons having assigned functions are provided with a mouse. The various mapped regions of the touchpad may be associated with the assigned functions of the mouse.
A primary disadvantage of using prior art touchpads as input devices is that the touchpads do not incorporate actual pressure data in their control signals. It is desirable to control the rate that a computer performs a function in proportion to the amount of actual pressure being applied to the input device. For example, if a user presses down in a scroll control region wanting a graphical user interface display to scroll, it is desirable that the rate of scrolling is proportional to the amount of pressure applied. In short, more pressure should cause faster scrolling.
Furthermore, prior art touchpads are not user friendly. For instance, many portable touchpads include a button on the bottom of the touchpad which, when pressed, is used to emulate the selection function of the button on a mouse. When the user desires to drag the cursor across the display, the button must be held down. When the cursor must be moved relatively long distances, necessitating multiple touchpad strokes, it is difficult to hold the drag button down to prevent release of the button and termination of the drag sequence while accomplishing the multiple strokes. If the finger is simply lifted from the touchpad, the drag sequence terminates and must be restarted. Even if the cursor can be dragged with a single touchpad stroke, it is extremely difficult to maintain sufficient pressure on the touchpad to hold the button down while sliding a finger across the touchpad. Consequently, in using touchpads for dragging, the drag sequences are frequently unintentionally terminated.
Summary of the Invention
Accordingly, it is an object of the present invention to provide a touchpad having the ability to measure the actual pressure applied by an object and the location of the object touching the touchpad.
It is a further object of the present invention to provide a force sensing semiconductive touchpad.
It is another object of the present invention to provide a force sensing semiconductive touchpad having the ability to determine the position of an object touching the touchpad.
It is yet a further object of the present invention to provide a force sensing semiconductive touchpad having the ability to measure the gradation of pressure applied on the touchpad and offer dynamic pressure-sensing features.
It is yet another object of the present invention to provide a force sensing semiconductive touchpad that requires minimal power consumption.
It is still yet a further object of the present invention to provide a force sensing semiconductive touchpad having the characteristics of requiring minimal amount of force to be activated, not subjecting a user to fatigue, and not susceptible to inadvertent cursor positioning.
It is still yet another object of the present invention to provide a force sensing semiconductive touchpad that is unaffected by ordinary amounts of moisture occurring during use.
A further object of the present invention is to provide a force sensing semiconductive touchpad that uses cheap and simple electronic circuitry for determining the position and applied pressure of an object touching the touchpad.
Another object of the present invention is to provide a touchpad that provides a control signal having actual pressure data to a computer so that the computer performs a function in proportion to the amount of actual pressure being applied to the touchpad.
Still, a further object of the present invention is to provide a touchpad that is user friendly.
Still, another object of the present invention is to provide a touchpad having separate control regions linked to separate functions.
Still, yet a further object of the present invention is to provide a touchpad capable of gesture recognition for supporting single tap select gesture, double tap execute gesture, and tap and drag dragging gesture to simulate actions done on a mouse button.
Still, yet another object of the present invention is to provide a touchpad having edge continuation motion for allowing large cursor excursions with a relatively slight single gesture.
In carrying out the above objects, the present invention provides a touchpad for providing a signal to a computer. The signal is indicative of the location and applied pressure of an object touching the touchpad. The touchpad includes a pad having a touch surface and a bottom surface. A first sensor layer is disposed adjacent the bottom surface of the pad. A first pair of spaced apart conductive traces runs across opposite ends of the first sensor layer in a first direction such that a first resistance between the opposite ends of the first sensor layer connects the first pair of conductive traces.
The touchpad further includes a second sensor layer. A second pair of spaced apart conductive traces runs across opposite ends of the second sensor layer in a second direction generally perpendicular to the first direction such that a second resistance between the opposite ends of the second sensor layer connects the second pair of conductive traces. The second sensor layer is disposed beneath the first sensor layer such that the first and second sensor layers come into contact at a contact point when an object asserts a pressure on the touch surface of the pad. The contact point is connected to each conductive trace by a variable pressure resistance associated with the first and second sensor layers and variable position resistances of the first and second sensor layers. The variable pressure resistance varies inversely as a function of the pressure asserted and the variable position resistances vary proportionally as a function of the distance of the contact point from the conductive traces.
The touchpad may further include a first pair of timing capacitors each connected to a respective one of the first pair of conductive traces and a second pair of timing capacitors each connected to a respective one of the second pair of conductive traces. The touchpad may also include a microprocessor operative with the timing capacitors for controlling and monitoring charging time of the timing capacitors to determine the position and asserted pressure of the object on the touch surface of the pad.
Further, in carrying out the above objects, a method for providing a signal to a computer representative of a position and asserted pressure of an object touching a touchpad is provided. The method is for use with a touchpad having X and Y position and Z pressure sensitive sensor layers in which the X and Y sensor layers come into contact at a contact point when the object touches the touchpad. The method includes providing a pair of spaced apart X conductive traces running across opposite ends of the X sensor layer along a Y direction such that a resistance RX between the opposite ends of the X sensor layer connects the pair of X conductive traces. Then a pair of spaced apart Y conductive traces running across opposite ends of the Y sensor layer along an X direction generally perpendicular to the Y direction is provided such that a resistance RY between the opposite ends of the Y sensor layer connects the pair of Y conductive traces is provided.
The X conductive traces are then driven to a given voltage so that current flows from the contact point through a variable pressure resistance RZ across variable position resistances to the pair of Y conductive traces. The position of the object is then determined along a Y direction on the Y sensor layer as a function of the current flowing from the contact point to the pair of Y conductive traces. The current varies as a function of the variable pressure resistance RZ and the variable position resistances connecting the pair of Y conductive traces to the contact point.
The Y conductive traces are then driven to a given voltage so that current flows from the contact point through a variable pressure resistance RZ across variable position resistances to the pair of X conductive traces. The position of the object is then determined along an X direction on the X sensor layer as a function of the current flowing from the contact point to the pair of X conductive traces. The current varies as a function of the variable pressure resistance RZ and the variable position resistances connecting the pair of X conductive traces to the contact point. The Z pressure of the object touching the touchpad is then determined from the currents flowing from the contact point to the pairs of X and Y conductive traces.
Determining the position of the object along the X and Y directions may be performed by determining the time required for the current to charge timing capacitors connected to the respective ones of the X and Y conductive traces.
The advantages accruing to the present invention are numerous. For instance, the touchpad of the present invention provides a touchpad for providing a signal to a computer indicative of the location and applied pressure of an object touching the touchpad. The touchpad has the ability to measure the gradation of pressure applied on the touchpad and offer dynamic-sensing features.
These and other features, aspects, and embodiments of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings.